1. Field of the Invention
The present invention relates to a method for capping a lamp such as various types of incandescent lamps, a high-pressure discharge lamp, a bulb-shaped fluorescent lamp or the like.
2. Description of the Prior Art
Conventionally, in the case where an E-type base is used as the base of a bulb-shaped lamp such as various types of incandescent lamps, a high-pressure discharge lamp and a bulb-shaped fluorescent lamp, plasma arc welding is performed to connect a base eyelet and the end of a lead wire in the center. This method is disclosed in JP 62-73552A and JP 56-30247A.
The conventional method for capping a lamp has the following problems. In the case of a E26 base that is most commonly used for a bulb-shaped lamp, the diameter of the hole through which the lead wire is drawn out of the eyelet is about 1 to 1.6 mm. On the other hand, a lead wire having a relatively small diameter of about 0.1 to 0.5 mm that can act as a fuse for the purpose of improving safety, such as a monel wire, has been used increasingly. Therefore, it has been difficult to fill the hole of the eyelet completely with a molten portion of the lead wire by plasma arc welding, because the difference between the diameter of the hole of the eyelet and the diameter of the lead wire is too large.
FIG. 3 is a view showing the conventional manner in which a base eyelet and a lead wire are connected. As shown in FIG. 3, when the diameter of the hole 9 of the eyelet 5 of the base 2 is excessively large relative to the diameter of the lead wire 8, the molten portion 12 of the lead wire cannot completely fill the hole 9 of the eyelet, and an opening 13 may be generated in the center. Another problem is that the lead wire 8 and the eyelet 5 cannot be welded completely and firmly. Incomplete welding results in poor weld strength, and contamination of foreign substances or poor appearance reduces the commercial value of the product. Thus, the product is not practically usable. On the other hand, if the diameter of the hole 9 of the eyelet is made small, it may be difficult to carry out automatic insertion of the lead wire 8.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a method for capping a lamp that can achieve complete plasma arc welding between a lead wire and a base eyelet and that improves weld strength.
A method for capping a lamp of the present invention includes drawing out a lead wire from a hole of a base eyelet of a bulb-shaped lamp and fusing the eyelet and the lead wire by plasma arc welding, and is characterized in that a conductive metal piece is supplied to the vicinity of a portion at which the eyelet and the lead wire are fused, and then plasma arc welding is performed. This embodiment allows the supplied conductive metal piece to be molten during plasma arc welding and welded with the base eyelet completely. Therefore, even if the hole diameter of the base eyelet is excessively large relative to the diameter of the lead wire, the hole of the base eyelet can be closed completely with a satisfactory appearance, and the lead wire and the eyelet can be connected completely and firmly.
In the above embodiment, it is preferable to provide a holder having a funnel-shaped portion above the eyelet, and to supply the conductive metal piece into the funnel-shaped portion. This embodiment allows the conductive metal piece to be held in the funnel shaped-portion of the holder until plasma arc welding starts, so that automatic capping of a lamp can be performed easily. Furthermore, selecting an appropriate shape of the funnel shaped-portion allows the conductive metal piece to be supplied easily to the vicinity of the portion to be welded. Thus, the present invention allows automatic production of bulb-shaped lamps and improves productivity. In addition, it is not necessary to modify conventional equipment significantly, because a conductive member that conventionally has been used for plasma arc welding can be used with minor modifications of its shape or the like as the holder.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.